An MS/MS analysis (or tandem analysis) is a type of mass-analyzing method using an ion trap mass spectrometer or similar apparatuses. In a typical MS/MS analysis, an ion having a specific mass (m/z) is first separated from the material to be analyzed. This ion is called the parent ion, or the precursor ion. Next, the precursor ion thus separated is broken into fragment ions by a collision-induced dissociation (CID) process. Finally, the fragment ions (called the “fragment ions” hereinafter) produced by the dissociation process are subjected to a mass-analyzing process to obtain information about the mass or chemical structure of the ion concerned.
In recent years, such apparatuses have been often used to analyze samples having larger molecular weights and more complex structures (or compositions) than before. Some samples having special characteristics cannot be broken into ions having adequately small weights by a single dissociating step. One method for dealing with such a case is called the MSn analysis, in which the dissociating operation is repeated multiple (n−1) times and the fragment ions finally produced are subjected to a mass-analyzing process (for example refer to Patent Documents 1 and 2). If, as in the previous case, the dissociating operation is performed just once, the mass analysis of the fragment ions can be called the MS2 analysis.
In the MSn analysis, candidates for the molecular structure or composition of the original sample are narrowed down on the basis of two kinds of information: a composition formula expressed by a combination of the elements estimated from the mass of the precursor ion; and a combination of the elements estimated from the mass of the fragment ions. In this case, even an apparatus capable of calculating masses with a considerable level of accuracy will encounter a larger number of candidates as the molecular weight becomes larger. Then, it will be very difficult to finally determine the composition of the sample concerned.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. H10-142196
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2001-249114